Electronic device manufacturers strive to produce a rich interface for users. Conventional devices use visual and auditory cues to provide feedback to a user. In some interface devices, kinesthetic feedback (such as active and resistive force feedback) and/or tactile feedback (such as vibration, texture, and heat) is also provided to the user, more generally known collectively as “haptic feedback” or “haptic effects.” Haptic feedback can provide cues that enhance and simplify the user interface. Specifically, vibration effects, or vibrotactile haptic effects, may be useful in providing cues to users of electronic devices to alert the user to specific events, or provide realistic feedback to create greater sensory immersion within a simulated or virtual environment.
Haptic feedback has also been increasingly incorporated in portable electronic devices, such as cellular telephones, smartphones, portable gaming devices, and a variety of other portable electronic devices. For example, some portable gaming applications are capable of vibrating in a manner similar to control devices (e.g., joysticks, etc.) used with larger-scale gaming systems that are configured to provide haptic feedback. Further, devices such as smartphones use haptic effects to cause “buttons” on a touchscreen to feel like their mechanical counterparts when selected by a user.
In order to generate vibration effects, many devices utilize some type of actuator/motor or haptic output device. Known actuators used for this purpose include an electromagnetic actuator such as an Eccentric Rotating Mass (“ERM”) actuator in which an eccentric mass is moved by a motor and rotates around an axis of rotation. However, because of inertia, the mass in an ERM takes time to get up to the desired rotation speed, and time to wind back down. This “spin up” and “spin down” time can cause latency in the generation of vibratory type haptic effects, and can degrade the “feeling” of haptic effects. In particular, multiple haptic effects that are generated within a short span of each other, such as in response to multiple “keypad” presses, can “cascade” or pile up into a continuous “buzz” due to the latency with slow, inexpensive ERMs.